Fire and heat radiation damper

ABSTRACT

A radiation shield means for limiting the transfer of heat by radiation is provided for a fire damper having a curtain wall shiftable from an open damper position allowing air flow through an opening in the damper to a closed position in which the curtain wall blocks air flow through the damper opening. Preferably, the curtain wall is formed with reversely folded and hinged damper blades and the radiation shield means comprises a pair of asbestos fabric sheet shields loosely tucked into the blades for stowage and for unfolding into generally planar sheets with shifting of the damper blades into a curtain wall position. The fabric shields are disposed on opposite sides of the damper blades and have loose and minimal contact therewith and with the blades define a pair of air spaces. A coating retains the asbestos fibers against liberation into an air stream flowing through the damper opening.

O United States Patent [1 1 [111 3,861,443

Tarnoff Jan, 21, 1975 FIRE AND HEAT RADIATION DAMPER PrimaryExaminer-Philip C. Kannan [75] Inventor: Sherwin S. Tarnoff, Northbrook,Ill. 33:52:2 Agent or Flrm Fltch Evan Tabm & [73] Assignee: Air Balance,Inc., Chicago, Ill.

[22] Filed: Aug. 3, 1973 [57] ABSTRACT [21] Appl' N05 385,475 Aradiation shield means for limiting the transfer of heat by radiation isprovided for a fire damper having 521 U.S. c1 160/1, 160/34, 160/35, aCurtain Shiftable from Open damper Position 160/84, 2 allowing air flowthrough an opening in the damper to [51] Int. Cl Ef /20 a closedPosition in which the curtain Wall blocks air 58 Field of Search 160/16, 34, flow through the damper p Preferably, the

160/35 4 R, 235 232; 12 /2 290 tain wall is formed with reversely foldedand hinged damper blades and the radiation shield means com- [5References Cited prises a pair of asbestos fabric sheet shields looselyUNITED STATES PATENTS tucked into the blades for stowage and forunfolding into generally planar sheets with shifting of the Q damperblades into a curtain wall position. The fabric 86683O 9/1907 Vance /235X shields are disposed on opposite sides of the damper 3 401734 9/1968blades and have loose and minimal contact therewith 3,687,185 3/1972Singer u and with the blades define a pair of air spaces. A coat-3,690,080 9/1972 Dillard 160/84 R x g ins the asbestos f bers againstliberation into an air stream flowing through the damper opening.

7 Claims, 7 Drawing Figures PATENTEBJANZI I975 SHEET 2 [IF 2 FIRE ANDHEAT RADIATION DAMPER This invention relates to fire dampers and moreparticularly to fire dampers having a metal curtain wall movable from anopen condition in which air may flow through an opening in the damper toa closed position in which the curtain wall substantially blocks theflow of air and smoke or fire through the damper opening.

Fire dampers of this genenral kind usually include a square orrectangular frame for fitting in an air duct and are usually installedeither in a vertical position as in a vertical wall or in a horizontalposition as in a ceiling or floor. In some instances, the curtain wallmay be made of a single piece of steel, but a preferred curtain wallconstruction comprises several foldable damper blades hinged alonglongitudinally extending edges thereof for pivoting between a folded,stacked position allowing air to flow through the damper and anunfolded, extended curtain wall position blocking air flow through thedamper. Herein, the invention is described in connection with a folding,hinged blade fire damper as disclosed in US. Pat. No. 3,327,764.

More specifically, a folded stack of hinged blades is held adjacent oneend or the top of the damper frame by a heat releasable means, such as afusible link which melts when exposed to high temperature. Release ofthis means occasioned by high temperature allows the blades to drop andunfold to block air flow through the damper. In horizontalinstallations, springs are connected to the blade assembly to pull theblades across the damper opening when the fusible link or othertemperature actuated means releases the blades for unfolding. Invertical installations, gravity may suffice to close the damper. As theblades move to form the curtain wall, each pivots about its connectionwith an adjacent blade with the blades moving generally into a flatplanar curtain wall.

Fire dampers of the aforementioned kind usually have steel blades and asteel frame, which provides good structural strength to maintain thecurtain wall closed to any substantial flow therethrough of smoke, fireand heated air when the damper is exposed to high temperature fires andwhen streams of water from fire hoses are played theragainst. These firedampers have met widespread commercial acceptance and have proven verysatisfactory. However, there are occasions requiring fire dampers whichare not only effective in blocking the flow therethrough of fire, hotair, and smoke but which also effectively limit heat transfer byradiation to alleviate the likelihood of ignition of or failure ofstructural materials on the other side of the fire damper from the heatsource. Generally speaking, steel fire dampers of the aforementionedkind have failed to meet Underwriters Laboratories, Inc. radiation testsat high temperatures as the steel blades do not reduce sufficiently theradiation heat transfer through the damper.

Accordingly, a genral object of the present invention is to provide anew and improved fire damper capable of severely limiting the transferof heat by radiation across the damper.

Other objects and advantages of the invention will become apparent fromthe detailed description taken in connection with the accompanyingdrawings in which:

FIG. 1 is a cross-sectional view of the fire damper with its curtainwall in the closed position and embodying the novel features of theinvention;

FIG. 2 is a cross-sectional view similar to FIG. 1 but with the curtainwall in the open position;

FIG. 3 is a front elevational view of the fire damper shown in FIG. 2;

FIG. 3A is a cross-sectional view taken along the line 3A-3A of FIG. 3.

FIG. 4 is a cross-sectional view of another fire damper with its curtainwall in the closed position and embodying the novel features of theinvention;

FIG. 5 is a cross-sectional view similar to FIG. 4 but with the curtainwall in the open pdsition; and

FIG. 6 is a plan view of the fire damper shown in FIG. 4.

As shown in the drawings for purposes of illustration, the invention isembodied in a fire damper I1 having a frame 12 with means in the form ofa metal curtain wall 13, as best shown in FIG. 1. The curtain wall 13 ismovable between the closed position shown in FIG. 1 in which the curtainwall closes an opening 14 (FIG. 3) through the rectangular frame 12 andan open position, as best seen in FIGS. 2 and 3, in which the curtainwall is folded to the top of the frame and exposes the opening 14,thereby allowing the flow of air through the damper. The frame istypically of rectangular shape with a first pair of verticallyextending, parallel side frames or walls 17 and 18 joiined at oppositeends to a second pair of parallel horizontally extending top and bottomwalls 19 and 20. Herein, the curtain wall 13 comprises a plurality ofmetal damper blades 22 pivotally mounted at respective longitudinallyextending edges 23 to an adjacent blade or blades, as fully described inUS. Pat. No. 3,327,764, for moving between the unfolded or unstackedposition, shown in FIG. 1, and the folded or stacked position shown inFIGS. 2 and 3.

The curtain wall 13 is held in the open position by a releasablesecuring means 34, which may take several forms, but herein isillustrated as including a pair of depending straps 25 carrying afusible link 26 extending across the bottom of the lowermost blade 22.The fusible link will, on the occurrence of excessive heat as 0ccasionedby a fire and at a predetermined temperature, melt, releasing the bladesto move to the closed position forming the curtain wall as shown in FIG.1, closing the opening 14 and confining the fire. In other instances, aheat sensor located at a remote location may actuate means to releasethe link 26, thereby releasing the blades 22 to shift to the closedposition. When the frame 12 is in a vertical position, the blades 22 maydrop under the force of gravity; however, when the frame 12 is installedin a horizontal position as will be described in connection with theembodiment illustrated in FIGS. 4, 5 and 6, the blades are released tobe shifted by the forces of springs 27 to the closed position.

In the closed curtain wall position, the damper blades 22 are generallyadequate to block the flow of hot air and smoke therethrough,particularly when equipped with smoke seals along the side edges of theblades for sealing against air flow, as disclosed in US. Pat. No.3,729,043. Although heat transfer through the thin steel blades isrelatively good, the damper blades 22 are not usually touching anythingexcept the frame 12 and hence heat is not transferred from the blades toany great extent. On the other hand, heat transfer by radiation may bequite large, particularly where a very high temperature, e.g., 1,800F.,is present on one side of the fire damper. Also, the blades may bucklewhen the temperature of the blades if allowed to become very high andcreate spaces between or about the blades thereby allowing air to flowthrough the curtain wall. In some tests, it has been found thatsufficient heat is transferred across the fire damper by radiation toignite materials or to cause the failure of structural materials on theside of the damper opposite from the heat source. Preferably, the firedamper should be effective in blocking heat transfer by radiation,convection and conduction as well as having sufficient structuralintegrity at high temperatures to resist impingement of high velocitystreams of water. As cost is always an important factor, the solution tothe problem of protection of radiation heat transfer across the dampershould preferably be simple and inexpensive.

Heretofore, in fire dampers as described in the aforementioned patents,a fire on one side of the damper transferred heat by convection andradiation directly to the steel blades and the steel blades being a goodradiator of heat radiated heat from the other side of the damper andpermitted transfer by convection, even while blocking the flow of hotair, smoke and fire through the damper opening 14. Some very old patentsin the art such as U.S. Pat. No. 827,677 suggested the use of asbestossheets or coatings on the damper blades to insulate the same. But thesehave at least two drawbacks, and this solution is not known to be in useat the present time. Asbestos fibers from the coatings are dangerous toones health and are not usually allowed in air moving equipment; andattaching of the asbestos directly to the steel blades results inconsiderable heat transfer by conduction through the asbestos to or fromthe blades. Another suggestion in U.S. Pat. No. 685,481 is to provide afabric or coating with rolled damper blades and would be subject to theobjections of fiber generation and heat transfer by conduction to orfrom the blades. These also leave the hinged joints uncovered.

In accordance with the present invention, improved resistance to heattranfer and particularly to heat transfer by radiation and convection isprovided in a fire damper by spacing at least one radiation shield 30 or31 from an adjacent side of a metallic curtain wall 13 to definetherewith an air space 32or 25 when the shield is extended with thecurtain wall 13 to cover the opening 14 through the damper. Preferably,a pair of radiation shields 30 and 31 are used on opposite sides of thecurtain wall 13, and they preferably are fireproof fabric sheets such aswoven asbestos fabric sheets having a surface coating to severely retardor stop erosion of asbestos fibers therefrom by the flowing air stream.

Heat transfer by conduction from the upstream radiation shield, forexample, the shield 30, to the facing flat sides 33 of the blades 22 isseverely limited because of the small area of contact, if any, betweenthe shields 30 and the blades 22 and because of the loose contacttherebetween. The same condition between the other sides 37 of theblades 22 and the facing fabric shield 31 also results in little heattransfer by conduction to and through the radiation shield 31 to thother side of the damper. Preferably, one or both of the radiationshields 30 and 31 are held taut when extended to reduce the likelihoodof the shield conforming to or laying against large surface areas of thecurtain wall 13.

Because of the generally small dead air spaces 32 and 35, heat transferby convection to or from the spaces on either side of the damper from orto the blades 22 is limited, and the heat transfer by convection betweenan adjacent radiation shield 30 or 31 and a blade facing side 33 or 37is not great. Also, as will be explained in greater detail, the tworadiation shields 30 and 31 reflect radiant heat and effectively dividethe fire damper into a plurality of successive re-radiation zones orsections with a plurality of temperature drops therebetween. As a resultof these re-radiation zones, the total effect of radiant heattransferred is, as may be calculated by using Stefan-Boltzmans law,considerabaly reduced from prior art dampers without such re-radiationzones. These greater numbers of re-radiation and temperature drop zonesresult in successively lower maximum radiation temperatures at each ofthe successive heat radiating surfaces; and, because radiation accordingto Stefan-Boltzmans law depends upon the difference between the fourthpower of the temperatures of the radiating surfaces, the result ofreducing temperature differentials becomes a very significant factor inthe overall amount of heat transferred.

Assuming a fire is on one side of the damper and raises a temperature Ton a first side of the damper to a relatively high temperature, forexample l,800F., the heat from the fire is transferred by radiation andconvection to exterior surface 39 of the radiation shield 30 and heat isthen conducted by conduction therethrough to the interior surface 41 ofthe radiation shield 30 to raise its temperature to a temperature T,.The heated interior shield surface 41 will radiate the heat to thefacing surface 33 of the metal blades 22. Relatively little heat istransferred to the blades 22 by conduction for the reason that there isrelatively little, if any, contact between the blades 22 and theinterior surface 41 of the asbestos shield 30. Even at the points ofcontact between the shield 30 and the blade interconnections 23, thereis relatively little force or pressure contact between the shield 30 andthe blades 22 as would provide a good heat conductive path. From thestandpoint of heat transfer by convection, the space 32 is generallyintended to be a small closed air space with any air flow circulatingtherein by natural convection being relatively slow moving and withoutachieving a good scrubbing of surface air at the interior shield surface41. The net result is a low convection heat transfer between theinterior surfaces 41 of the shield 30 and the facing surfaces 33 of theblades 22.

The damper blades 22 being good conductors of heat will readily transmitheat by conduction from one side or surface 33 to its opposite side orsurface 37. The blade surfaces 37 are likewise spaced generally by thedead air space 35 from the radiation shield 31 and have a low heattransfer by convection therebetween for the reasons given above. Heattransfer by conduction from the blade surfaces 37 to the radiationshield 31 is small because of small engaging surface areas and the lackof tight, interrnate contact with the blades 22 and the shield 31.

The blade surfaces 37 which are at a temperature T transmit heat byre-radiation to the interiorly facing surface 45 of the radiation shield31 heating the latter to a temperature T Heat will flow through theshield 31 by conduction to the opposite exterior side 47 thereof. Heatis re-radiated therefrom to the surrounding atmosphere to raise thetemperature on the other side of the fire damper to a temperature T Thestatement that the radiation shields 30 and 31 have loose and-littlecontact with the blades 22 does not exclude substantial and intimatecontact with a top blade 2217 at the top wall 19 and a bottom blade 22aas these locations are protected or hidden by depending flanges 40 ofthe top frame walls 19 and by upwardly projecting flanges 42 of thelower frame wall and are generally outside of the re-radiating blades atthe opening 14 in the damper. While heat is tranferred to and throughthe frame and therefrom, this quantity of heat transsferred has notresulted in a failure of the illustrated damper in acutal radiationtests, as described herein. As will be explained, these manners ofconnection of the shields 30 and 31 to the frame 12 and to the curtainwall 13 are simple and low in cost.

Without the radiation shields 30 and 31, the temperature drop across theradiation damper was generally T T and T T with there being relativelylittle reflection of the radiant heat by the blades 22. As there were nodead air spaces in these prior art dampers, air could sweep and scrubthe blades 22 on both sides thereof and transfer heat readily byconvection between the areas at temperatures T and T Also, as thetemperatures T and T remained relatively high, the multiplying of thesetemperatures to the fourth power will demonstrate the magnitude ofgreater heat transfer by radiation without radiation shields 30 and 31than with the radiation shield 30 and 31 which, e.g., provide fourtemperature drops and transfer zones, viz., zones T T T T T T T TTherefore, it will be seen that because of the reduced heat transfer byconduction, convection and radiation through the illustrated firedamper, there results a lower temperature on the side of the fire damperopposite from the fire with the damper having radiation shields 30 and31 than for a similar fire damper without such radiation shields.

The illustrated radiation shields 30 and 31 extend the width of theblades 22 and into opposite channels 51 each defined between a pair ofblade guide flanges 53 and 54 which project inwardly from the verticalside walls 17 and 18 of the damper frame. In some instances, theradiation shields may shift outwardly from behind an edge of one of theflanges 53 or 54, but the shield will still retain their effectiveness.In this preferred embodiment of the invention, the radiation shields 30and 31 are both formed from a single piece of asbestos woven fabricwhich has a first end 55 at the top wall 19 of the frame and extendsdownwardly to define the radiation shield 30 to an integral bottomportion 56 looped about the underside of the lowermost damper blade 22a.The bottom portion 56 is integral with the radiation shield 31 and this,in turn, extends to a second end 57 for the asbestos fabric, which endis disposed beneath the overlapping first end 55 of the fabric. The ends55 and 57 of the asbestos fabric are sandwiched and captured between thetop damper blade 22b and the top wall 19 by a pair of fasteners 59, suchas rivets. The latter secure the blade tightly to the frame and hold thefabric ends parallel and aligned so that opposite edges 60, FIG. 3, ofthe fabric are parallel to the frame side walls 17 and 18 when thedamper blades 22 are in the closed position. The bottom portion 56 ofthe fabric may also be secured to the bottom blade 22a by a series offasteners 61 to assure proper positioning of the radiation shields 30and 31 across the opening 14. Preferably, the length of the respectiveshields is related to the final position of the lower blade 22a, whenthe curtain wall is in the closed position, such that the shields 30 and31 are relatively taut and have minimal contact with the blades andmaintain the dead air spaces 32 and 35. The fabric is thus positionedbetween te top blade and the top frame wall 19 and between the bottomblade and the bottom frame wall 20 thereby reducing the heat transfer byconduction from the prior art damper consturction in which metal bladesabutted the metal top and bottom frame walls 19 and 20.

In accordance with the present invention, the radiation shields 30 and31 are in a stowed condition above the opening 14 by being nested orfolded between adjacent blades 22. When the blades 22 fall from thedamper open position shown in FIG. 2, the fabric unfolds to provide thegenerally planar sheet-like radiation shields 30 and 31 each extendingthe width and height of the damper opening 14. Herein, the shields 30and 31 also extend above and below the opening 14. In the stowageposition, as best seen in FIG. 2, the shield 30 is folded with the foldplies or portions 30a and 30b tucked between each of the pairs ofadjacent folded blades 22; and in a like manner the fabirc shield 31 isfolded with fold plies or portions 31a and 31b tucked between a pair ofrespective adjacent blades 22.

When the fire damper is installed in a vertical position as shown inFIGS. 1-3, the weight of the metal fire curtain 13 is normallysufficient to insure the dropping of the lowermost portion thereof suchas the lowermost blade 22a to the bottom wall 20 of the frame 12 and tocarry the fabric shields 30 and 31 downwardly therewith while unfoldingthe same. However, in horizontal installations, such as in a ceiling,springs 27 (FIG. 4) are provided to pull the curtain wall 13 to theclosed position. In this instance, each of a pair of springs 27 isfastened to an outer end of the lowermost damper blade 22a by one of therivets 61 which also serve to fasten the lower loop of the fabric to thebottom blade 22a. The spring 27 are usually metal negator springs whichare disposed in the opposite channels 51 adjacent the side walls 17 and18 of the frame for winding about spools 63. The spools 63 are disposedat the bottom of the channels 51 and fastened to the side walls 17 and18, as best seen in FIG. 6, near the bottom frame wall 20. The dampershown in FIGS. 4-6 is identical to the damper shown in FIGS. 1-3 exceptthat the springs 27 and spools 63 have been added thereto and hencecommon reference characters have been used for both embodiments of theinvention.

The preferred asbestos fabric is obtainable from Raybestos-Manhattan,Inc. of Elmhurst, Illinois and is tightly woven asbestos fabric which isprovided with a fiber retention coating such as, for example, a coatingof polyurethane to limit fiber liberation from the fabric by the movingair stream. This decreases the fiber deposition into the air streamflowing through the damper opening 14. Under recent health and safetycodes, asbestos fiber materials, which have been found to be injuriousto health, are regulated, particularly for use in air moving equipmentor in air ducts such as a fire damper air duct installations in whichstreams of moving air may abrade or erode fibers from the shield. Inaccordance with the present invention, the polyurethane coating ispresent on both sides 39 and 41 of the radiation shield 30 and bothsides 45 and 47 of the radiation shield 31. Such coatings of the entireasbestos fabric have reduced the amounts of asbestos fibers liberated towell below acceptable levels and to as low as 0.0015 particles per cubiccentimeter.

Although in the event of fire, the polyurethane coating melts whensubjected to the high temperatures contemplated herein, the melting ofthe coating does not adversely affect the heat transfer limitingqualities of the radiation shields 30 and 31 and of the damper 11.Preferably, the asbestos fabric is formed with a tight weave so thatafter the coating melts, the radiation shields 30 and 31 remainsufficiently impermeable to substantially block air flow therethroughand thereby limit heat transfer by convection through the pores of thefabric. That the coating is destroyed by fire and thereupon liberatesthe asbestos fibers is not significant as the radiation shields stillfunction effectively for their intended purpose. The release of asbestosfibers during the emergency is negligible, and the asbestos fabric willnot be used again after the emergency. The fire damper will be replacedor repaired. The weave of the asbestos fabric is sufficiently tight ifthe fabric stops convection flow to blades as the closed blades of thecurtain wall prevent any direct air flow through the damper and theasbestos fabric need not be so tight as to perform this function. Itwill be appreciated that other fire resistant materials may be used forthe radiation shields 30 and 31 than that described above and still fallwithin the purview of the present invention.

A fire damper of the general type described herein has successfullysurvived a radiation best for Underwriters Laboratories in which thedamper 11 was mounted horizontally in a ceiling. The ceiling was formedof fire resistant tiles and it was spaced by a plenum chamber, in whichan air duct was mounted, from an overhead floor slab which was supportedby members extending upwardly from the ceiling. in this UnderwritersLaboratories test, the temperature in the room (T is approximately1,800F. and the test is continued until either a component fails or thetemperature (T in the plenum reaches l,000. In this test, the firedamper ll successfully blocked heat transfer therethrough as would raisethe plenum temperature to 1,000F. for a 2 hour period; and, after 2hours, but before reaching a l,0OF air temperature in the plenum,another component of the ceiling-floor-slab test assembly failed. Basedon present knowledge, it is expected that in a similar test with betterceiling-floor-slab materials that the damper 11 should pass at least afour-hour test before l,000 F air temperature is attained in the plenum.

From the foregoing, it will be seen that the present invention providesan improved fire damper particularly resistant to radiation heattransfer. Because the steel curtain will can withstand high temperaturesand provides a structural rigidity, the fire damper may be mounted in avertical wall to pass fire hose tests in which a water discharge from awater hose is blocked by the blade assembly. Moreover, the damper of thepresent invention may use coated asbestos fabric for radiation shieldswithout liberation of large quantities of asbestos fibers in the airstream flowing therethrough.

While a preferred embodiment has been shown and described, it will beunderstood that there is no intent to limit the invention by suchdisclosure but, rather, it

is intended to cover all modifications and alternate constructionsfalling within the spirit and scope of the invention as defined in theappended claims.

What is claimed is:

1. A fire damper comprising a frame having a pair of side walls and topand bottom walls joined to said pair of side walls and encompassing anopening through which air may flow; a metal curtain wall meansassociated with said frame and movable from an open damper positionpermitting air to flow through said opening to a closed positionsubstantially closing the opening in said frame to air flowtherethrough, a first radiation shield positioned in a stowage conditionleaving said opening exposed and movable therefrom to an effectiveposition for covering said opening, said first radiation shield beingdisposed on one side of the curtain wall means and generally spacedtherefrom when the latter is in its closed position, a second radiationshield positioned in a stowage condition leaving said opening exposedand movable therefrom to an effective position for covering saidopening, said second raidiation shield being disposed on the oppositeside of said curtain wall means and generally spaced therefrom when thelatter is in its closed position, and means holding said curtain wallmeans in said open position and said radiation shields in the stowagecondition and operable in response to high temperatures to release saidcurtain wall means for movement to said closed position and saidradiation shields to said effective positions.

2. A fire damper in accordance with claim 1 in which said first andsecond radiation shields each comprise an asbestos fabric sheet and inwhich a coating on said sheets retains fibers of asbestos from freeliberation into an air stream flowing through said opening.

3. A fire damper in accordance with claim 1 in which said curtain wallmeans is comprised of a plurality of elongated metal damper bladeshingedly connected together at parallel longitudinally extending edges,said blades being reversably foldable and stackable in said open damperposition, and in which said radiation shields each have portions thereoftucked between said folded blades when the latter are in said opendamper position.

4. A fire damper in accordance with claim 3 in which said first andsecond radiation shields comprise integrally connected portions of anasbestos woven fabric and in which folds are formed in said fabric bytucking said fabric between adjacent facing blades when the blades arein the open damper position.

5. A fire damper in accordance with claim 4 in which a plastic coatingcovers said asbestos fabric to prevent erosion of the asbestos fibersfrom the fabric.

6. A fire damper in accordance with claim 3 in which said radiationshields comprise asbestos fabric sheets no more than loosely contactingsaid blades except for the topmost and bottomost blades and coveringsaid opening when said curtain wall is in the closed position.

7. A fire damper in accordance with claim 6 in which sasid sheets aresecured to the top one of said damper blades and to said top frame walland to the lowermost one of said blades.

1. A fire damper comprising a frame having a pair of side walls and topand bottom walls joined to said pair of side walls and encompassing anopening through which air may flow; a metal curtain wall meansassociated with said frame and movable from an open damper positionpermitting air to flow through said opening to a closed positionsubstantially closing the opening in said frame to air flowtherethrough, a first radiation shield positioned in a stowage conditionleaving said opening exposed and movable therefrom to an effectiveposition for covering said opening, said first radiation shield beingdisposed on one side of the curtain wall means and generally spacedtherefrom when the latter is in its closed position, a second radiationshield positioned in a stowage condition leaving said opening exposedand movable therefrom to an effective position for covering saidopening, said second radiation shield being disposed on the oppositeside of said curtain wall means and generally spaced therefrom when thelatter is in its closed position, and means holding said curtain wallmeans in said open position and said radiation shields in the stowagecondition and operable in response to high temperatures to release saidcurtain wall means for movement to said closed position and saidradiation shields to said effective positions.
 2. A fire damper inaccorDance with claim 1 in which said first and second radiation shieldseach comprise an asbestos fabric sheet and in which a coating on saidsheets retains fibers of asbestos from free liberation into an airstream flowing through said opening.
 3. A fire damper in accordance withclaim 1 in which said curtain wall means is comprised of a plurality ofelongated metal damper blades hingedly connected together at parallellongitudinally extending edges, said blades being reversably foldableand stackable in said open damper position, and in which said radiationshields each have portions thereof tucked between said folded bladeswhen the latter are in said open damper position.
 4. A fire damper inaccordance with claim 3 in which said first and second radiation shieldscomprise integrally connected portions of an asbestos woven fabric andin which folds are formed in said fabric by tucking said fabric betweenadjacent facing blades when the blades are in the open damper position.5. A fire damper in accordance with claim 4 in which a plastic coatingcovers said asbestos fabric to prevent erosion of the asbestos fibersfrom the fabric.
 6. A fire damper in accordance with claim 3 in whichsaid radiation shields comprise asbestos fabric sheets no more thanloosely contacting said blades except for the topmost and bottomostblades and covering said opening when said curtain wall is in the closedposition.
 7. A fire damper in accordance with claim 6 in which sasidsheets are secured to the top one of said damper blades and to said topframe wall and to the lowermost one of said blades.